1. Field of the Invention
This invention relates to a fitting-type connection terminal used in electric wiring in an automobile, an industrial equipment and so on.
2. Related Art
Generally, in electric wiring used in an automobile, an industrial equipment and so on, tinning has heretofore been applied to a fitting-type connection terminal used for connecting wires together. The purpose of this is that when connecting the terminals together, an oxide film on the surface of the tin film is destroyed by friction, thereby causing fresh tin to adhere to the terminal, so that a low contact resistance can be stably obtained.
In electric wiring used in a particularly-important signal circuit, for example, for an ABS (anti-lock braking system) and an air bag, connection terminals have been plated with gold.
The above adhesion of the tin film is due to the low hardness of tin (Vickers hardness of 40 to 80). However, the low hardness of tin invites a problem that an increased insertion force is required when connecting the terminals together. Namely, during the fitting connection of the terminal, the tin film is worn by adhesion, and the terminal is fitted against the deformation resistance of tin, so that the insertion force is increased.
Incidentally, in electric wiring in an automobile and so on, it is a common practice to connect a bundle of wires (hereinafter referred to as "wire harness") by the use of only one connector, and the force required for connecting the connector can be estimated by multiplying an insertion force, required for one terminal, by the number of wires (conventionally, 10 to 20 poles). Therefore, if the insertion force per terminal is high, the force required for the connection of the connector becomes a large value corresponding to the number of wires of the wire harness.
Particularly, recently, with the marked advance and development of car electronics, the number of electronic devices and CPUs, mounted on an automobile, has greatly increased, and therefore the number of wires of the wire harness has increased, and it has been eagerly desired to achieve a multi-pole design of a connector (e.g., 30 to 40 poles).
However, as described above, in the case of the multi-pole design of the connector, the force required for the connection of the connector increases in proportion to the number of the wires, and the connection of the connector can not be effected without the use of an auxiliary mechanism such as a bolt and a lever. Therefore, even if the terminal is formed into a small size, the auxiliary mechanism prevents the compact, lightweight design of the connector.
One proposal to reduce the insertion force for the terminal is to reduce a contact pressure (i.e., pressing force applied to a contact point at a fitting portion). In this case, however, a stable, low contact resistance can not be obtained. In other words, it is difficult to reduce the terminal insertion force while maintaining the stable contact resistance, and therefore the auxiliary mechanism becomes indispensable when forming the connector into a multi-pole design, and this prevents the compact, lightweight design of the connector.
When gold is plated on the connection terminals, the low contact resistance can be obtained even with the low contact pressure, and therefore the terminal insertion force can be reduced, and the force, required for the connection of the connector, is not much increased. However, the cost of the gold plating is several times to several tens of times higher than the cost of the tinning, and therefore this is not suitable particularly for the multi-pole connector.